1. Field of the Invention
This invention relates to a brazing clad material, and a brazing method and a brazing product using the same. In particular, this invention relates to a brazing clad material that is used to braze a member of a heat exchanger, fuel cell etc.
2. Description of the Related Art
Stainless base clad materials are used as a bonding material for automobile oil cooler. It is composed of a stainless steel sheet as a base material, and a copper material which is cladded on one or both surfaces of the stainless steel plate and serves as a brazing material.
Various Ni brazing materials with excellent corrosion resistance at a brazing joint part are specified by JIS (Japanese Industrial Standards) as a brazing material for a member which is made of stainless steel, Ni-based or Co-based alloy etc.
For example, JP-A-2000-107883 discloses a powdered Ni brazing material for heat exchanger that comprises 4 to 22 wt % of metal powder selected from Ni, Cr or Ni—Cr alloy.
JP-A-7-299592 discloses a self-brazing composite material that has a brazing material laminar structure of Ni/Ti/stainless steel, in which a brazing material layer made of Ni and Ti is formed on the surface of a base material of stainless steel.
However, when the conventional brazing material or brazing clad material is used as a brazing material in brazing a heat exchanger such as a cooler of fuel cell reformer or exhaust gas recirculation (EGR) which is exposed to high-temperature and corrosive gas or liquid, the following problems may occur.
(1) When the abovementioned stainless base clad material is used as a brazing material for the automobile oil cooler, there is no problem in heat resistance and corrosion resistance. However, when the stainless base clad material is used as a brazing material for the cooler of fuel cell heat exchanger or EGR, there is a problem in corrosion resistance. Namely, since high-temperature and corrosive solution or exhaust gas is circulated in the cooler of fuel cell heat exchanger or EGR, the brazing material, i.e., the copper material, is insufficient in corrosion resistance.
(2) The self-brazing composite material, i.e., the Ni—Ti clad material as disclosed in JP-A-7-299592 may be subjected to “erosion of base material” that a component of the base material is melted into (diffused into) the brazing material in brazing. In such a case, the base material will be significantly eroded by the brazing material such that it decreases in thickness. As a result, a problem will be caused that strength at the brazing joint part lowers.
(3) The powdered Ni brazing material as disclosed in JP-A-2000-107883 or the Ni brazing materials as specified by JIS are in powder form. Therefore, the powdered Ni brazing material needs to be coated on each brazing joint part. Thus, the brazing work needs a large amount of labor and the productivity of the brazing product lowers significantly. This causes an increase in manufacturing cost. Further, since amorphous Ni brazing materials specified by JIS are very fragile, they are difficult to handle in producing the brazing material and in assembling the brazing product. The manufacturing cost increases as well.